ObjectivesThe need for training programs and certification processes in fetal ultrasound has become obvious. The purpose of this study was to evaluate the feasibility of a score-based quality control system for fetal biometry in the second trimester.
Methods
The aim of this study was to elucidate the pituitary adjustments implicated in photoperiodic control of reproduction in two mammalian species, the ferret and the mink. In the ferret, which displays renewed testicular activity when the days lengthen, we observed a stimulation of the pulsatile liberation of luteinizing hormone (LH) reflecting the pulsatile activity of the gonadotropin-releasing hormone (GnRH) system when daylight was equal to or in excess of LD 8:16. This photoperiod coincides precisely with the phase of photosensitivity known to be essential for gonadal stimulation in this species. In the mink, which displays renewed testicular activity when the days shorten, pituitary stimulation was activated when daylight was reduced to LD 11:13, and gonadal stimulation occurred only when daylight was further reduced to LD 10:14. In addition to requiring different photoperiodic stimuli to trigger the seasonal reproductive process, the two species display variations in the "timing" of pituitary control of renewed gonadal activity.
In the male edible dormouse, it has been proposed that the annual temperature cycle is the major external factor triggering annual biological rhythms in this hibernating species. The present study was designed to explore (i) the effects of suppression of the annual thermoperiodic cycle under natural photoperiodic conditions, and (ii) the effects of acute exposure to a warm environment on basal plasma T4 levels observed during hibernation. The results of the first experiment demonstrate an absence of circannual cycles of hibernation, body weight, and endocrine thyroid and gonadal functions in the absence of annual fluctuations of temperature (constant warm environment at 24 degrees C) despite the maintenance of a normal photoperiodic cycle. On the other hand, acute exposure to 24 degrees C during the late stage of hibernation stimulated thyroid function as expressed by a consistent transitory rise in plasma T4 concentrations, which was maximal within 7 days and restored to basal levels after 14 days. These findings are in close agreement with the concept that in the edible dormouse, the annual thyroid cycle is synchronized with the annual temperature cycle. Moreover, the present study, combined with prior data indicating that the thyroid cycle induces the testis cycle, suggests that the ambient temperature cycle may be intricately involved in the control of neuroendocrine cycles in dormice, although the mechanism is still unknown.
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